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Old 12th February 2013, 02:08 PM   #1
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Default 1959 RCA tube amplifier needs help

Hello guys I'm new to this about tube amplifiers and I found this schematic from a 1959 RCA book "PDF" and I would like to give it a try, I build solid states amplifier but also I like to learn tube amplifiers, I basically copied the schematic the best I can so if some one can help me out verified is all is ok on this circuit, and yes, I do understand that voltages on tube amplifiers are lethal and can be really dangerous but I'm aware of that I will be careful, "alligator clips all the time", I have found the correct power transformer yesterday and the tube too, the RCA 7199 if I'm correct is no longer in reproduction anymore, so the 6U8 is the substitution for it but just minor wiring has to be modified to fit the 6U8, the RCA 7027-A tube not sure about this I think it also can use 6L6 tubes not sure, about this schematic I just need to know if there is something that might be incorrect or if there is a wrong power supply voltages, I copied the best I can, but I will really appreciate if some one can help me out verified is everything is ok I will leave the scheamatic here in PDF and image format if you want it to add or put notes to it, I will really appreciated any help.

Regards
Juan
Attached Images
File Type: png RCA High Fidelity Amplifier Circuits.PNG (603.9 KB, 274 views)
File Type: jpg RCA 30 watt HF amp.JPG (777.9 KB, 272 views)
File Type: png ghj.PNG (345.8 KB, 256 views)
File Type: png llj.PNG (769.1 KB, 241 views)
Attached Files
File Type: pdf RCA 30 watt HF amp.pdf (732.4 KB, 39 views)

Last edited by vargasmongo3435; 12th February 2013 at 02:20 PM. Reason: add words
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Old 12th February 2013, 02:24 PM   #2
Cassiel is offline Cassiel  Libya
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I think you should copy the ST70 circuit.

Welcome to Dynaco-ST70.com Restoration and Repairs services
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Old 12th February 2013, 02:36 PM   #3
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Wow sir! you surely make beautiful restorations awesome job!, but that means this RCA circuits is not that good? I can copied that one sure, you also have the power supply circuit too?

Regards
Juan
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Old 12th February 2013, 02:48 PM   #4
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WOW thank you sir there is a lot of info about this ST70 circuit.

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Juan
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Old 12th February 2013, 02:58 PM   #5
Cassiel is offline Cassiel  Libya
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Yeah, that's why I said you should copy it. It's proven and it sounds good. The one you posted may be a better circuit -it's anyone's guess. My guess is that it's not. Besides, the output tubes are not that common anymore. That ST70 web page is not mine by the way, just linked so you could see the schematic.
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Old 12th February 2013, 03:06 PM   #6
rmyauck is offline rmyauck  Canada
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If you get Triode Electronics Dynaco ST-70 PCB board you will get the same type of circuit with easy to find in production tubes. They sometimes show the schematic also. You can run many different output tubes with some mods. Dynaco used a simplified Williamson circuit on all it's amps which that RCA also is.

Some of the popular Dynaco ST-70 boards out there use the Mullard 5-20 circuit like the Eico HF-87/89 & HF50 These are other circuits to look at. diytube.com sells PCB's for the Eico/Mullard type circuit. The Eiclone has everything on one PCB for the supposed to be great sounding Eico HF-87/89

Other popular PCB's with the Mullard circuit are sold by classicvalvedesign.com along with original Dynaco PCB's Tubes4hifi is another popular affordable choice. These last 2 companies have gone with SS CCS on their boards. dynakitparts also sells original type PCB's also. The last 2 companies also have all the Dynaco schematics and manuals on their web site also.

I think you may prefer fixed bias also. The Dynaco ST-70 & Eico amps used it except the HF-87 which is cathode bias and that RCA amp also has it. You get more power out of fixed bias also, but you do have to check the bias and set it from time to time.

All the aftermarket Dynaco boards are fixed bias.

The reason I brought up the aftermarket boards is that most use in production tubes and are well liked and supported. You could always find the schematic for them and do a P2P version if you want also.

Hope that helps!

Randy

Last edited by rmyauck; 12th February 2013 at 03:33 PM.
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Old 12th February 2013, 03:13 PM   #7
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Oh well I thought that old RCA will be good, but I guess a already tested unit will be better for me to begging with, I seen a lot of info about this amp ST-70 they have the boards on EBay and many other parts,thank you guys.

Regards
Juan
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Old 12th February 2013, 06:39 PM   #8
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just a note about the RCA circuit above: it uses a 7199 and 7027 which aren't exactly cheap, unless you don't mind the newer Russian stuff. Personally I would something cheap like a TV Sweep tube, or something really common like the EL34.
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Old 12th February 2013, 07:00 PM   #9
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As suggested Dynacos ST70 and Eico HF-87/89 & HF50 might be way too out of my hand because of the cost, but those models have a lot of reading material and information about mod and people comments are really in favor for those models mentioned here, I like both models ST70 and Eico HF-87/89 & HF50 actually 4 but is sad that there is not much info about this RCA 30 amplifier, so mister kstagger "TV Sweep tube, and EL34." will work on this RCA vintage schematic? oh by the way I do not mind use Russian tubes, they can be Americans, Germans, what ever work the best I do not mind I just want to build it as my first project to get experience , "I'm a solid state guy" but it will be a honor to represent tube amplifiers, but I really appreciate your input guys I think I'm getting there maybe ST70 is too overkill for my first try but is good to know that is really popular kit many were sold, thank you guys again.

Regards
Juan

Last edited by vargasmongo3435; 12th February 2013 at 07:05 PM.
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Old 12th February 2013, 08:28 PM   #10
rmyauck is offline rmyauck  Canada
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If 17W/CH is enough maybe the Dynaco ST-35 clones would be in your budget. diytube.com has version using more common in production tubes for more choices while still using the original circuit. They sell PCB's for $10 less than triode electronics which has a kit version. You could always diy a chassis to save$.

dynakitparts sells orgional boards.

The great Z-565 output transformer clones were first made by triode electronics and magnaquest transforms makes runs every so often. dynakitparts recently started selling their clones.

Anyway many prefer the ST-35 to the ST-70. The great sounding EL84/6BQ5 tubes help there also.


You can also drive the just as easy to drive 7591/7868 tubes that EH & JJ now make again with the same circuit. You can get an easy 30W/CH.
You would also use close to 7K output trans. with fixed bias , but preferably rated for more power.

I don't think tubes cost is that big an issue for the amps mentioned as the in production aren't much more than the sweep tubes, and will always be oibtainable.

Transformer cost is the main issue with tube amps as good or great sonically Output Ones cost more $.



Randy

Last edited by rmyauck; 12th February 2013 at 08:32 PM.
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